Presently, there are a number of non-emissive display devices on the market. One of those display devices is the liquid-crystal display (LCD), which uses the polarization properties of the liquid-crystal molecules to block a light beam or to allow the light beam to transmit through. The polarization properties of the liquid-crystal molecules are controllable by an electric field generated by a pair of electrodes disposed on a pixel. The major disadvantages of the LCD include the relatively slow switching time and that the light beam passing through the liquid crystal layer must be polarized. A polarized beam reduces the light efficiency of the device.
It is advantageous and desirable to provide an imaging or display device that does not require polarized light and has fast switching time.
Levola (U.S. Pat. No. 6,445,433 B1) discloses a projection system that uses an imaging lens with a beam stop to focus light reflected from a light-valve structure in order to form an image on a projection screen. In particular, the light-valve structure has a layer of reversibly deformable material disposed between a glass plate and a silicon backplane active matrix, as shown in FIGS. 1a and 1b. A section of the light-valve structure is shown in FIGS. 2a and 2b. As shown, a transparent electrode layer is disposed on the lower surface of the glass plate and an electrode array disposed on top of the silicon backplane for applying an electric field on the deformable material. When the electric field is off, the upper surface of the transparent deformable material is substantially flat, as shown in FIG. 2a. An illumination beam will pass the transparent deformable layer unaltered, reflect off the electrode structure and propagate toward the projection screen as it would when reflecting from a plane mirror (see FIG. 1a). When the electric field is turned on, the deformable material is deformed to form ripples on the upper surface, as shown in FIG. 2b. These ripples can cause a locally varying phase change in the beam that is passing through the deformable material and reflected of the electrode structure. As a result, part of the light beam reflected by the electrodes is diffracted due to these phase variations and is directed away from the lens stop (see FIG. 1b). With the imaging lens, light that avoids the lens stop can be focused to form an image on a projection screen, for example. Thus, when the electric field is off, the pixel on the light valve structure as seen on the projection is “black” or “dark”, because substantially no light reflected from that pixel avoids the beam stop. But when the electric field is on, the pixel on the light valve structure as seen on the projection screen is “white” or “bright”. Basically, this projection system is a Schlieren optical system, which forms an image based on spatially shifted light.
In particular, the deformable material used in the light-valve structure is a dielectric, viscoelastic gel, as disclosed in Schrader (WO 02/091059 A1) and Glenn (U.S. Pat. No. 4,626,920). Partially depending on the thickness of the material layer that forms the pixel, the switching time between a “white” state and a “black” state is much shorter than the switching time of a liquid crystal material with comparable thickness. Furthermore, another advantage of the deformable material over the liquid crystal material is that polarized light is not necessary in an optical system that uses the deformable material as a light-valve.
Thus, it is desirable and advantageous to use this dielectric, viscoelastic, deformable material in a display device that can be viewed with the naked eye without the aid of a projection device.